An air pressure regulator provides a fluid pressure output which varies with an input signal. Pressure regulators have many usages which require that the regulated pressure be very accurately controlled. One example is in the testing of pneumatic instruments, such as an air speed indicator, an altimeter, and a rate of descent meter for an aircraft. It is also necessary to test the systems in which these instruments are used. The test must accurately simulate the air pressure these instruments encounter during actual inflight conditions, and this requires that the air pressure regulator provide air pressure above and below ambient pressure.
One prior art system for pressure regulators utilizes two regulators, one for pressures above ambient and one for pressures below ambient. Each regulator uses a flexible, resilient valve strip folded between a swing arm and a port. By pivoting the swing arm, the valve strip is moved to progressively close or open the port. The differential pressure across the port tends to seat the valve strip against the surface surrounding the port.
The use of a folded valve strip is most effective in a pressure regulator. Unfortunately, the prior art system described above requires two of the regulators, and this substantially increases the cost and complexity of the system.
My U.S. Pat. No. 3,994,314 discloses a pressure regulator which solves the problems noted above. My prior pressure regulator utilizes two separate U-shaped valve strips constructed of rubber. The rubber strips are used to cover and uncover ports which communicate with sources of fluid at positive and negative pressures, respectively. These rubber strips must be relatively thick to provide sufficient force to tightly seal against the ports. Unfortunately, these relatively thick rubber strips have a high hysteresis, and accordingly, the regulator is not as accurate as it would be if the hysteresis were eliminated.
Secondly, bending of the relatively thick rubber strips places the interior of the curve in compression and the exterior of the curve in tension. This results in a groove or concavity being formed over at least a portion of the exterior surface of the rubber strip. This groove may cause leakage at some positions of the rubber strip.